Core mantle boundary topography from short period PcP, PKP, and PKKP data     

Edmond K.M. Sze  Robert D. van der Hilst 《Physics of the Earth and Planetary Interiors》2003,135(1):27-46

We use a total of 839,369 PcP, PKPab, PKPbc, PKPdf, PKKPab, and PKKPbc residual travel times from [Bull. Seism. Soc. Am. 88 (1998) 722] grouped in 29,837 summary rays to constrain lateral variation in the depth to the core-mantle boundary (CMB). We assumed a homogeneous outer core, and the data were corrected for mantle structure and inner-core anisotropy. Inversions of separate data sets yield amplitude variations of up to 5 km for PcP, PKPab, PKPbc, and PKKP and 13 km for PKPdf. This is larger than the CMB undulations inferred in geodetic studies and, moreover, the PcP results are not readily consistent with the inferences from PKP and PKKP. Although the source-receiver ambiguity for the core-refracted phases can explain some of it, this discrepancy suggest that the travel-time residuals cannot be explained by topography alone. The wavespeed perturbations in the tomographic model used for the mantle corrections might be too small to fully account for the trade off between volumetric heterogeneity and CMB topography. In a second experiment we therefore re-applied corrections for mantle structure outside a basal 290 km-thick layer and inverted all data jointly for both CMB topography and volumetric heterogeneity within this layer. The resultant CMB model can explain PcP, PKP, and PKKP residuals and has approximately 0.2 km excess core ellipticity, which is in good agreement with inferences from free core nutation observations. Joint inversion yields a peak-to-peak amplitude of CMB topography of about 3 km, and the inversion yields velocity variations of ±5% in the basal layer. The latter suggests a strong trade-off between topography and volumetric heterogeneity, but uncertainty analyses suggest that the variation in core radius can be resolved. The spherical averages of all inverted topographic models suggest that the data are best fit if the actual CMB radius is 1.5 km less than in the Earth reference model used (i.e. the average outer core radius would be 3478 km).  相似文献   

A fluid-pressure feedback model of dehydration reactions: experiments, modelling, and application to subduction zones   总被引：3，自引：0，他引：3  

S. A. Miller  W. van der Zee  D. L. Olgaard  J. A. D. Connolly 《Tectonophysics》2003,370(1-4):241-251

Dehydration and melting reactions generate large volumes of fluid in the crust and upper mantle, and play an important role in subduction zone seismicity. The fluid pathway must evolve from isolated pockets in low porosity, low permeability rock, coalescing to interconnected permeable pathways to the surface. When fluid pressures generated from a dehydration or melting reaction are sufficient to induce hydrofracture, then hydrofracture significantly influences the porosity–permeability structure within the dehydrating/melting horizon. If a low fluid-pressure boundary is introduced to the dehydrating rock, then fluid will be driven from the rock along the evolved permeable network toward that boundary. The resulting pressure reduction can then accelerate the dehydration reaction and further drive the flow. The sudden introduction of a low fluid-pressure boundary may occur by the co-seismic (dilatant) rupturing of a pressure seal that connects different fluid pressure states. This mechanism is invoked to explain the observed post-seismic evolution of wave velocities (V_p/V_s) following the 1995 Antofagasta, Chile earthquake. We show experimental results and introduce a conceptual and numerical model that reflects this scenario. The model couples the mechanical and thermodynamic effects of fluid pressure with devolitization kinetics, and is quantitatively consistent with experimental studies of the dehydration of gypsum and serpentine. The experimental results show that dehydration is controlled by access to a free (drained) boundary. The model provides a mechanistic explanation for the experimental observations and has applications in understanding the role of transient transport networks on the large-scale behavior of dehydrating and melting systems.  相似文献   

Preface     

Conall Mac Niocaill  Trond Torsvik  Ben van der Pluijm 《Tectonophysics》2003,362(1-4):vii-x

  相似文献   

Modelling of hydrocyclone performance based on spray profile analysis     

J. S. J. van Deventer  D. Feng  K. R. P. Petersen  C. Aldrich 《International Journal of Mineral Processing》2003,70(1-4):183-203

Spray profile measurements can be used to calculate the underflow rate, and consequently, be related to hydrocyclone performance. The flow geometry of the spray discharge is found to arise from velocity patterns at the outlet orifice. Through a videographic example of an industrial hydrocyclone, it is shown that underflow profiles are typically parabolic, a feature which is indicative of the velocity at which the fluid exits. The inclusion of gravity in this model clearly highlights deficiencies in currently used models. Moreover, an intimate knowledge of factors affecting the profiles of the underflow of a cyclone is essential for the correct interpretation of videographic images. Subsequently, image data are used to estimate outlet velocities, which give an excellent insight into various fluid mechanical phenomena that are not appreciated by analysing basic operational variables. The exit velocities are used to calculate underflow rates, which are related to mass recovery in the underflow.  相似文献   

Editorial     

Jérôme Jaffré  Mary Fanett Wheeler  Hans C. J. van Duijn 《Computational Geosciences》2003,7(4):251-252

  相似文献   

The Lower Wonderfontein Spruit: an exposé     

C. Swart  E. Stoch  C. van Jaarsveld  A. Brink 《Environmental Geology》2003,43(6):635-653

During the nineteenth century the Wonderfontein Valley and Spruit were described as a 'natural jewel' by adventurers. The valley underlain by dolomitic aquifers contained copious volumes of water and partly overlies gold-mining excavations, which were under a threat of flooding. For safety and economic reasons, large-scale dewatering of some of the dolomitic aquifers was decided upon as a matter of policy. This led to the lowering of the water table, which accelerated the formation of sinkholes and dolines in geologically sensitive areas. The streambed along approximately the first 30 km of the Lower Wonderfontein Spruit is particularly vulnerable. The mining sector attempted to rehabilitate the affected parts of the streambed by filling the sinkholes with various materials. Unfortunately, many of the treated sinkholes were reactivated by storm flow.  相似文献   

Accuracy assessment of InSAR derived input maps for landslide susceptibility analysis: a case study from the Swiss Alps   总被引：2，自引：0，他引：2  

Lalan P. Singh  C. J. van Westen  P. K. Champati Ray  P. Pasquali 《Landslides》2005,2(3):221-228

In recent years SAR interferometry has become a widely used technique for measuring altitude and displacement of the surface of the earth. Both these capabilities are highly relevant for landslide susceptibility studies. Although there are many problems that make the use of SAR interferometry less suitable for landslide inventory mapping, it’s use in landslide monitoring and in the generation of input maps for landslide susceptibility assessment looks very promising. The present work attempts to evaluate the usefulness and limitations of this technique based on a case study in the Swiss Alps. Input maps were generated from ERS repeat pass data using SAR interferometry. A land cover map has been generated by image classification of multi-temporal SAR intensity images. An InSAR DEM was generated and a number of maps were derived from it, such as slope-, aspect, altitude- and slope form classes. These maps were used to generate landslide and rockfall susceptibility maps, which give fairly well acceptable results. However, a comparison of the InSAR DEM with the conventional Swisstopo DEM, indicated significant errors in the absolute height and slope angles derived from InSAR, especially along the ridges and in the valleys. These errors are caused by low coherence mostly due to layover and shadow effects. Visual comparison of stereo images created from hillshading maps and corresponding DEMs demonstrate that a considerable amount of topographic details have been lost in the InSAR-derived DEM. It is concluded that InSAR derived input maps are not ideal for landslide susceptibility assessment, but could be used if more accurate data is lacking.  相似文献   

Three-dimensional elastic scattering by near-surface heterogeneities     

Christina D. Riyanti  Gérard C. Herman 《Geophysical Journal International》2005,160(2):609-620

  相似文献   

Dictators and their capital cities: Moscow and Berlin in the 1930s     

Herman van der Wusten 《GeoJournal》2001,52(4):339-344

Stalin and Hitler planned major changes in the townscapes of their capital cities. These plans were part of their effort to install highly mobilized despotic regimes that needed a wide-ranging set of symbols to focus allegiance and to impress awe. These plans remained to some extent paper exercises but part of it left significant traces in the contemporary cities, particularly in Moscow. The intended changes showed similarities in their megalomania expressed in plans for a gigantic dome surrounded by a huge public square in the core of the city. There were also differences as regards the type of symbols used due to both dictotors' different roles within their regimes, the degree of didactic intent due to the nature of the commanding ideologies and the level of modernization of both countries, and the diverging versions of antimodernist building style (which they shared with many others elsewhere at the time).  相似文献   

Fe–Mg partitioning between ringwoodite and magnesiowüstite and the effect of pressure, temperature and oxygen fugacity     

D. J. Frost  F. Langenhorst  P. A. van Aken 《Physics and Chemistry of Minerals》2001,28(7):455-470

 The partitioning of Mg and Fe between magnesiowüstite and ringwoodite solid solutions has been measured between 15 and 23 GPa and 1200–1600 ^∘C using both Fe and Re capsule materials to vary the oxidation conditions. The partitioning results show a clear dependence on the capsule material used due to the variation in Fe³⁺ concentrations as a consequence of the different oxidation environments. Using results from experiments performed in Fe capsules, where metallic Fe was also added to the starting materials, the difference in the interaction parameters for the two solid solutions (W _FeMg ^mw−W _FeMg ^ring) is calculated to be 8.5±1 kJ mol⁻¹. Similar experiments performed in Re metal capsules result in a value for W _FeMg ^mw−W _FeMg ^ring that is apparently 4 kJ higher, if all Fe is assumed to be FeO. Electron energy-loss near-edge structure (ELNES) spectroscopic analyses, however, show Fe³⁺ concentrations to be approximately three times higher in magnesiowüstite produced in Re capsules than in Fe capsules and that Fe³⁺ partitions preferentially into magnesiowüstite, with K _{D Fe3+} ^ring/mw estimated between 0.1 and 0.6. Using an existing activity composition model for magnesiowüstite, a least–squares fit to the partitioning data collected in Fe capsules results in a value for the ringwoodite interaction parameter (W _FeMg ^ring) of 3.5±1 kJ mol⁻¹. The equivalent regular interaction parameter for magnesiowüstite (W _FeMg ^mw) is 12.1±1.8 kJ mol. These determinations take into account the Fe³⁺ concentrations that occur in both phases in the presence of metallic Fe. The free energy change in J mol⁻¹ for the Fe exchange reaction can be described, over the range of experimental conditions, by 912 + 4.15 (T−298)+18.9P with T in K, P in kbar. The estimated volume change for this reaction is smaller than that predicted using current compilations of equation of state data and is much closer to the volume change at ambient conditions. These results are therefore a useful test of high pressure and temperature equation of state data. Using thermodynamic data consistent with this study the reaction of ringwoodite to form magnesiowüstite and stishovite is calculated from the data collected using Fe capsules. Comparison of these results with previous studies shows that the presence of Fe³⁺ in phases produced in multianvil experiments using Re capsules can have a marked effect on apparent phase relations and determined thermodynamic properties. Received: 13 September 2000 / Accepted: 25 March 2001  相似文献